1. Field
The present disclosure generally relates to offshore drilling services and methods, and more specifically to an apparatus and method for employing a jet pump in an underwater drilling environment.
2. Description of the Related Art
In order to produce fluids such as oil, gas, and water from subterranean rock formations, a well is drilled into the fluid-bearing zone. Most wells are generally drilled with a drilling rig, a drill bit, a drill pipe, and a pump for circulating fluid into and out of the hole that is being drilled. The drilling rig rotates and lowers the drill pipe and drill bit to penetrate the rock. Drilling fluid, sometimes referred to as drilling mud, is pumped down the drill pipe through the drill bit to cool and lubricate the action of the drill bit as it disaggregates the rock. In addition, the drilling fluid removes particles of rock, known as cuttings, generated by the rotational action of the drill bit. The cuttings become entrained in the column of drilling fluid as it returns to the surface for separation and reuse.
One method for artificially inducing lift to remove fluids from a well by using a jet pump and a power fluid. The use of jet pumps is common in production operations where drilling activity has stopped. In this case, the drill pipe and drill bit have been extracted and a jet pump is lowered into the well on the end of a tubing string. A surface pump delivers high-pressure power fluid down the tubing and through the nozzle, diffuser, and diffuser of the jet pump. The pressure of the power fluid is converted into kinetic energy by the nozzle, which produces a high velocity jet of fluid. The drilling and production fluids are drawn into the diffuser of the jet pump by the stream of high velocity power fluid flowing from the nozzle into the diffuser of the jet pump. The drilling and production fluids mix with the power fluid as they pass through the diffuser. As the fluids mix, the diffuser converts the high velocity mixed fluid back into a pressurized fluid. The pressured fluids have sufficient energy to flow to the surface through the annulus between the production casing and the tubing that carried the jet pump into the well.
In offshore drilling the drill bit is sent into rock formations beneath the sea. The drill bit is affixed to drill pipe that travels inside a riser string. The riser string is formed of a number of riser joints. The use of heavy weight drilling mud creates a high well bore pressure. The high well bore pressure is created when the drilling begins because of the column of drilling fluid in the drill pipe extending from the drilling platform to the seabed. The high well bore pressure creates a number of problems. The drilling fluid may flow outward from the drill hole and into the earth, causing a breakdown the formation. Furthermore, as discussed above, fluids in the reservoir may flow into the well bore while the well is being drilled or after the well is drilled and during production.
Accordingly, it would be advantageous to have a method and system which takes into account one or more of the issues discussed above as well as possibly other issues.